Determination of histamine and identification of histamine-producing bacteria in frozen Longtail tuna (Thunnus tonggol)

Fish is considered as highly perishable food which spoils soon after death if not preserved properly. Consumption of spoiled fish results in the outbreaks of food poisoning such as histamine poisoning. Biogenic amines are the causative agents of histamine poisoning which are produced by various bacterial species. The aim of this study was to determine the amount of histamine and to identify the histamineproducing bacteria on frozen Longtail tuna (Thunnus tonggol) hunted from south of Iran. Microbial examinations and measurement of histamine were performed on the muscles around the gills of twenty five frozen samples. The results indicated that the mean ± SE Log CFU/g for total microbial and psychotrophic counts were 4.81 ± 0.26 and 4.66 ± 0.25, respectively. Different bacterial isolates were identified as histamine-producing bacteria i.e., Clostridium perfringens (24.4%) followed by Proteus spp. (23.0%), Klebsiella spp. (13.9%), and Enterobacter spp. (11.1%). Histamine content in 65.0% of the samples was more than the maximum acceptable level of 50 ppm. Therefore, there is a seafood safety risk in the current harvesting and post harvesting methods used in Longtail tuna industry.